1. Technical Field of the Invention
The present invention is directed to a control system for a magnetic levitation body such as a rotor of a magnetic bearing type spindle of a machine tool, a rotor of a turbo-molecular pump or a carrier levitation body of a magnetic levitation carrier system, which are all held afloat by magnetic forces.
2. Description of the Related Art
A levitating position of a magnetic levitation body (hereinafter simply referred to as a "levitation body") has heretofore been controlled by feeding back detection signals transmitted from position sensors.
In the case of, e.g., a rotor of a magnetic bearing type spindle, two parts of the rotor in the longitudinal direction are held afloat by magnetic forces of electromagnets, and levitating positions thereof in the radial and axial directions of the rotor are detected by position sensors. Detection signals of the position sensors are processed by a bridge circuit and other processing circuits, and exciting currents of the electromagnets are so controlled that the rotor is held afloat in a predetermined reference target position.
Problems to be Solved by the Invention
The following defects are, however, inherent in the above-described related art control system for a levitation body. Although the system is constructed to hold the levitation body afloat in a predetermined position by the feedback control, costs of production increase when manufacturing the levitation body in conformity with desired dimensions. Generally, there is more or less a scatter in the process of manufacturing the levitation body. The levitation body is not allowed to float in the predetermined target position due to this scatter, thereby making the levitating condition unstable.
Take a rotor of a machine tool for instance, a rotor diameter deviates slightly from a target value, and there are errors in assembly of electromagnets and the like. In such a case, the levitation body can not be levitated in an initially set target position, resulting in an unstable floating condition. This in turn causes inconveniences such as a drop in rigidity.